This invention relates generally to a system for the continuous withdrawal of blood and more particularly to a system for continuously withdrawing and collecting blood from a subject for a selected period. In order to analyze various properties of materials contained in blood, it is necessary that the blood be withdrawn from the subject. In some instances the blood concentration of material changes rapidly and markedly under physiological and pathological conditions. Values obtained from a single blood specimen, or even multiple blood specimens drawn in quick succession, will not reflect adequately the variations in concentration of the material.
For example, the integration of the concentration curves of hormones has been obtained previously by withdrawing numerous blood samples from a subject, measuring the concentration in each sample, and then calculating the average concentration. Use of this method results in inaccuracies in data collected and calculated as well as resulting in inconvenience and trauma to the subject due to the numerous blood withdrawals.
In an attempt to overcome these disadvantages, complex systems have been developed. For example, in one system, a pump withdraws blood continuously through an indwelling intravenous catheter and infuses by still another pump a heparin solution into the withdrawn blood through a small catheter inserted into an extracorporal portion of the indwelling catheter to prevent clotting in the withdrawal system. Obviously, the indwelling catheter must be larger than the infusion catheter and, therefore, is limited to indwelling in veins of considerable size. Also, two pumps are required and they must be closely synchronized. This and other similar systems require intricate arrangements and types of equipment which result in long periods of immobilization of the subject whose blood is being withdrawn.
Additionally, it is frequently necessary to determine the in vivo concentration of the diffusible fraction of certain materials in the blood. If the blood is withdrawn from the subject to measure, for example, the concentration of the diffusable part of any hormone, drugs or other material in the blood of the subject, the diffusible fraction, which may be 100% thereof, frequently changes once the blood is outside of the body. Therefore, intravenous sensing, rather than the analysis of withdrawn blood, is necessary to obtain accurate results.
In many systems where blood is withdrawn from a subject and conducted through various tubes and component parts of an analyzing system, the tubes and parts can be used only for relatively brief periods without clotting of the blood therein. This reduces the opportunity for long range blood withdrawal and the attendant advantages thereof.
It becomes apparent, then, that a need exists for a non-thrombogenic system for withdrawing blood from a subject over a relatively long period. In addition, there is a need for a non-thrombogenic system for permitting the determination of the in vivo concentration of various materials in blood. Additionally, there is an advantage in the portability of this combined system.
It is, therefore, an object of this invention to provide a system for the withdrawal of blood from a subject over and extended period of time to permit continuous analysis of the blood.
Another object of this invention is to provide a sensing system for permitting the continuous determination of the in vivo concentration of the diffusible fraction of certain materials in the blood as well as the continuous determination of the in vivo concentrations of non-diffusible materials in blood.
Yet another object of this invention is to provide a sensing system for permitting the continuous determination of the in vivo concentration of glucose in the blood.
Still another object of this invention is to provide a non-thrombogenic system which permits the continuous withdrawal of blood through a single catheter over an extended period of time.
Another object of this invention is to provide a nonthrombogenic system which will permit the measurement outside the system of the integrated concentration of a material in blood.
Still another object of this invention is to provide a portable system for the continuous withdrawal of blood from a mobile subject.
Other objects and attendant advantages of this invention will become more readily apparent and understood from the following detailed specification and accompanying drawings.